[Tutor] Python file escaping issue?

[Sithembewena Lloyd Dube]

@spr, thanks for the explanation, especially on representations of strings.
To think that i freely used repr(variable_x) without fully understanding the
meaning and the power of that function..



On Mon, Feb 22, 2010 at 9:37 AM, spir <denis.spir at free.fr> wrote:

> Just a little complement to Steven's excellent explanation:
>
> On Mon, 22 Feb 2010 10:01:06 +1100
> Steven D'Aprano <steve at pearwood.info> wrote:
>
> [...]
>
> > So if you write a pathname like this:
> >
> > >>> path = 'C:\datafile.txt'
> > >>> print path
> > C:\datafile.txt
> > >>> len(path)
> > 15
> >
> > It *seems* to work, because \d is left as backlash-d. But then you do
> > this, and wonder why you can't open the file:
>
> I consider this misleading, since it can only confuse newcomers. Maybe
> "lonely" single backslashes (not forming a "code" with following
> character(s)) should be invalid. Meaning literal backslashes would always be
> doubled (in plain, non-raw, strings). What do you think?
>
> > But if the escape is not a special character:
> >
> > >>> s = 'abc\dz'  # nothing special
> > >>> print s
> > abc\dz
> > >>> print repr(s)
> > 'abc\\dz'
> > >>> len(s)
> > 6
> >
> > The double backslash is part of the *display* of the string, like the
> > quotation marks, and not part of the string itself. The string itself
> > only has a single backslash and no quote marks.
>
> This "display" is commonly called "representation", thus the name of the
> function repr(). It is a string representation *for the programmer* only,
> both on input and output:
> * to allow one writing, in code itself, string literal constants containing
> special characters, in a practical manner (eg file pathes/names)
> * to allow one checking the actual content of string values, at testing
> time
>
> The so-called interactive interpreter outputs representations by default.
> An extreme case:
> >>> s = "\\"
> >>> s
> '\\'
> >>> print s, len(s)
> \ 1
> >>> print repr(s), len(repr(s))
> '\\' 4
> >>>
> The string holds 1 char; its representation (also a string, indeed) holds
> 4.
>
> > The best advice is to remember that Windows allows both forward and
> > backwards slashes as the path separator, and just write all your paths
> > using the forward slash:
> >
> > 'C:/directory/'
> > 'C:textfile.txt'
>
> Another solution is to take the habit to always escape '\' by doubling it.
>
>
> Denis
> ________________________________
>
> la vita e estrany
>
> http://spir.wikidot.com/
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-- 
Regards,
Sithembewena Lloyd Dube
http://www.lloyddube.com
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